Switch ok with debug mode apps, implement sys_exit correctly later.

user/Makefile

@@ -1,5 +1,5 @@
 TARGET := riscv64gc-unknown-none-elf
-MODE := release
+MODE := debug
 APP_DIR := src/bin
 TARGET_DIR := target/$(TARGET)/$(MODE)
 APPS := $(wildcard $(APP_DIR)/*.rs)
@@ -9,7 +9,7 @@ BINS := $(patsubst $(APP_DIR)/%.rs, $(TARGET_DIR)/%.bin, $(APPS))
 OBJDUMP := rust-objdump --arch-name=riscv64
 OBJCOPY := rust-objcopy --binary-architecture=riscv64
 
-elf:
+elf: $(APPS)
 	@python3 build.py
 
 binary: elf